1. Could you explain the significance of your article to the non-specialist?

When a molecule undergoes photodissociation it often results in the formation of atomic fragments that possess electronic angular momentum. It has been known for some time that this atomic angular momentum, whether it be spin and/or orbital in origin, can be polarized (i.e. can have a preferred direction in space), and that this polarization contains a wealth of information about the dissociation mechanism. In this article we discuss the recent progress that has been made in determining and interpreting such polarization effects, and illustrate this using a number of diatomic photodissociation case studies, both from our own group, and from others working in this area. 

2. What has motivated you to conduct this work?

Photofragmentation studies that involve the full characterization of M_J -level populations, and coherences between them, can be described as a 'complete experiment'. Such investigations yield all the observables that can be obtained by interrogating the photofragments. In the diatomic case, the extra information obtained by measuring the photofragment electronic angular momentum provides insight about the electronic states populated during dissociation, and about interference that can occur between different dissociation pathways leading to the same asymptotic products. Determining the polarization of the photofragments provides as close as one can get to a spectroscopic assignment of the dissociation mechanism. 

3. Where do you see this work developing in the future?

Measuring angular momentum polarization is quite a delicate task, and improvements in experimental techniques would be desirable to allow polarization moments to be determined with higher precision. As noted below, the main challenge at present is theoretical. There are very few systems for which polarization moments have been determined using exact theoretical methods, and thus far these have all been for diatomic molecules. 

4. Are there any particular challenges facing future research in this area? 

Electronic angular momentum polarization has now also been observed in a wide range of triatomic and polyatomic systems, and a very major challenge in the future is for theory to provide a quantitative explanation for the observed polarization. It seems reasonable to suppose that the polarization found for these larger systems will provide as much insight about the dissociation mechanism as in the diatomic case, but as yet the theoretical machinery is not sufficiently developed for such data to be easily interpreted.